Process for determining the temperature of a semiconductor wafer in a rapid heating unit

ABSTRACT

The invention relates to a process for determining at least one state variable from a model of an RTP system by means of at least one measurement signal measured on the RTP system—the measurement value—which has a dependency upon the state variable to be determined, and a measurement value forecast by means of the model—the forecast value—, whereby the measurement value and the forecast value respectively comprise components of a constant and a changeable portion, and whereby respectively at least the changeable portion is established, separated by a filter, so as to form a first difference between the changeable portion of the measurement value and the changeable portion of the measurement value forecast by the model, parameter adaptation of at least one model parameter by recirculation of the first difference in the model with the aim of adapting the model behavior to variable system parameters, forming of a second difference from the measurement value and the forecast value or from the measurement value adjusted by the changeable portion and the adjusted forecast value, state correction of a state of the model system by recirculation of the second difference in the model, with the aim of bringing the state of the model system into correspondence with that of the real system, and measurement of the at least one state variable on the model.

This specification for the instant application should be granted thepriority dates of Dec. 23, 2002, the filing date of the correspondingGerman patent application 102 60 673.0, Jun. 27, 2003, the filing dateof the corresponding German patent application 103 29 107.5, as well asNov. 28, 2003, the filing date of International patent applicationPCT/EP2003/013387.

BACKGROUND OF THE INVENTION

This invention relates to a process for determining at least one stateor condition variable from a model of an RTP system by means of at leastone measurement signal measured on the RTP system—the measurementvalue—which has a dependency upon the state variables to be determined.In particular, this invention relates to a process for determining thetemperature of an object, preferably a substrate such as e.g. asemiconductor wafer in a rapid heating unit whereby the object or thesubstrate is heated by radiation sources.

Rapid heating units for the thermal treatment of substrates such as e.g.semiconductor wafers are widely known in the production ofsemiconductors. They are used for the thermal treatment of wafers whichare preferably made from silicon but, however, can also be made fromcompound semiconductors such as e.g. II-VI, II-V and IV-IVsemiconductors. An important feature with the thermal treatment ofsemiconductor wafers in a rapid heating unit is accurate control andregulation of the wafer temperature during the thermal treatment. Thiscontrol and regulation of the wafer temperature requires, once again,accurate determination of the wafer temperature during the thermaltreatment in order to control or regulate the rapid heating unitcorrespondingly. This invention relates especially to the aspect ofdetermining the temperature of a semiconductor wafer during its thermaltreatment in a rapid heating unit. In general, the invention relates todetermining a state variable from a model of an RTP system whichdescribes the state of the RTP system by means of model parameters.

Different processes for determining the temperature of a semiconductorwafer in a rapid heating unit are known. On the one hand it is known toattach thermal elements to the semiconductor wafers themselves and/or inthe direct proximity of the same in order to establish theirtemperature. The problem arises here, however, that on the one hand, acomplex process is required in order to attach the thermal elements tothe semiconductor wafers, and on the other hand, they lead to localtemperature inhomogeneities because they generally have to remain inthermally conductive contact with the semiconductor wafers, andmoreover, effect the radiation field in the fast heating unit, at leastnear to the thermal element.

Another, contactless process which was made known, for example, in thepatent applications and patents DE-A-19852320, U.S. Pat. No. 6,191,392and U.S. Pat. No. 6,369,363 tracing back to the applicant, uses acontactless temperature measurement. With this contactless temperaturemeasurement a first pyrometer is provided which is directed to one sideof the wafer in order to collect radiation coming from the wafer whichcontains heat radiation from the wafer as well as radiation from theradiation sources reflected on the wafer. Furthermore, a secondpyrometer is provided which is directed towards the radiation sourcesthemselves in order to collect radiation coming from the radiationsources which is provided with a modulation. The modulation of theradiation sources is chosen here such that it does not effect the heatradiation of the wafer, but can be measured in the radiation from theradiation sources reflected on the wafer. Using a specific algorithm, itis possible to separate, to a certain extent, the heat radiation of thewafer measured on the first pyrometer from the radiation of theradiation source reflected on the wafer. The temperature of the wafercan then be determined from the heat radiation.

This type of temperature determination requires, however, two pyrometersor detectors, namely a so-called wafer pyrometer (or generally, adetector for measuring the radiation emitted from the wafer andreflected on the wafer or transmitted through the wafer) and a lamppyrometer (or a second measurement system for collecting the radiationemitted from the lamps or the radiation sources), which are respectivelyassociated with high costs. Furthermore, the lamp pyrometer or thesecond measuring system not only collects radiation originating from theradiation sources, but also partially radiation originating from thewafer, and this makes it difficult to accurately establish thetemperature of the semiconductor wafer and requires additional means foraccurately determining the lamp radiation, as described in the patentapplication DE-A-19852321 tracing back to the applicant. Additionalproblems arise with a high dynamic of the rapid heating system withregard to the temperature-time behavior of the wafer. If e.g. there arehigh heating rates of the wafer of over 250° C./sec., the radiationsignals of the heat emitters and of the wafer contain frequency portionsin the range of the modulation frequency. This results, among otherthings, in a falsification of the amplitude ratio established in thefrequency range from the radiation emitted from the heat emitters andmeasured by the wafer pyrometer. The transient measurement errors causedby this can have an extremely adverse effect upon the stability andperformance of the controlled system with a high dynamic. Thecontactless temperature determination with the help of modulatedradiation sources described above is therefore suitable, preferably forquasi-stationary systems, i.e. for systems or temperature-time processesto which the rapid heating unit wafer system is subjected which arequasi-stationary, i.e. in comparison to the modulation frequency of theradiation sources, they only change slowly with regard to time. Afurther problem results from the sensor sensitivity and from therequirements with regard to measuring accuracy because the contributionsof the modulated radiation are to be very accurately established,because by means of this, an in situ emissivity and/or transmissivitydetermination of the object (the wafer) takes place.

Starting from the above specified prior art, the task which forms thebasis of this invention is to provide a process for determining thetemperature of a semiconductor wafer in a rapid heating unit whereby thesubstrate is heated with a radiation source, which in a simple andcost-effective way makes it possible to reliably determine thetemperature of the semiconductor wafer. Furthermore, the task whichforms the basis of this invention is to determine a state variable of anRTP system, whereby especially, the state variable can be thetemperature of a semiconductor wafer in the rapid heating unit.

SUMMARY OF THE INVENTION

In accordance with the invention, the process for determining thetemperature of an object (preferably of a substrate such as e.g. asemiconductor wafer) in a rapid heating unit where the object (e.g. asemiconductor wafer) is heated with radiation sources (e.g. heatemitters), comprises the recording of an actuation value of theradiation sources, the recording of a measurement value, which isstrongly dependent upon the state value of an object in the rapidheating unit to be determined, or has sufficient dependency upon thestate value to be determined such as e.g. the temperature of the object(e.g. of the semiconductor wafer), determination of a forecast value forthis measurement value of the at least one object by means of a systemmodel of the rapid heating unit including a semiconductor wafer (object)which is acted upon by the actuation value of the radiation sources,determination of a state correction (in this application, also calledthe control value) for the system model from the difference between themeasurement value recorded and the forecast or predicted value of themeasurement value and determination of at least one state variable of astate of the semiconductor wafer and of a state of the system consistingof the semiconductor wafer and the rapid heating unit using the systemmodel and the state correction, whereby the determination of theforecast value of the measurement value takes place at least partiallyusing the determined state variables.

After applying the state correction, the model state corresponds verywell to the system state. The model therefore represents the state ofthe real system, and this is why the system state to be determined, suchas e.g. the wafer temperature, can be measured directly from the systemmodel.

This process makes it possible, in a simple and cost-effective way, todetermine at least one state variable of a state vector which preferablydescribes the state of the system consisting of the semiconductor waferand the rapid heating unit, whereby the temporal development of thesystem state and the reaction of the same to the actuation value aredescribed by a system model which preferably comprises several partmodels into which, on the one hand, at least one actuation value of therapid heating unit such as e.g. an actuation value of the radiationsources, and on the other hand, at least one specific state correction,are entered. In general, rapid heating systems are systems whereby thedifferent components with distributed system parameters and systemstates such as e.g. emissivity and temperature, have a complex thermalinteraction relationship to one another. The full description of thereal system would therefore involve a very large number of systemparameters and an accurate knowledge of the details of all thermalinteractions. For reasons relating to real time requirements, full modeldescriptions are therefore not generally feasible, and this is why thesystem models are preferably models reduced to the essential propertiesof the thermal system for the correct representation of the dynamic ofthe state variables of interest.

If one assumes that the initial state of the system model and of thereal system is exactly the same, that the system model exactlyillustrates the dynamic behavior of the real system, and that there areno interference values effecting the real system, the states of thesystem model and the real system would always develop in the same waywith the same actuation value. These assumptions are not realistic,however, and so the system model is supplemented by a control. Theoutput variables (measurement values) of the controlled path (realsystem) are compared with those of the system model (observer) anddifferences between them retroact by means of a controller on the stateof the observer. By means of this state correction (the retroaction ofthe difference between forecast values and measured values upon thestate and/or the parameters of the observer is also called the controlvalue or control parameter in this application), the state of theobserver is adapted to that of the real system, whereby the controllerminimizes the difference between the respective output values. Thesmaller the differences, the better at least the observed statevariables of the observer correspond to those of the controlled path (ofthe real system). If the temperature of a semiconductor wafer is thistype of observable state variable, it can be taken directly from thesystem model or measured from the same.

Or expressed differently, if for the state correction, the differencebetween the predicted value and the measurement value or the retroactionof the difference upon the state or the parameters of the observer isidentified as the control value or the control parameter for adaptationof the observer, i.e. the system model, the control value (or controlparameter) is determined by means of an algorithm which compares ameasurement value recorded for an object in the rapid heating unit witha forecast value of the measurement value of the object, and is intendedto minimize the difference between these two values. The smaller thedifference, the better the state variable, determined using the model,describes the actual state of the system consisting of a semiconductorwafer (object) and the rapid heating unit, and so also the state of theobject (semiconductor wafer), by means of which, as well as othervariables of this state, in particular the temperature of the object andof the semiconductor wafer can be determined.

In general, one can describe the dynamic behavior of a system by meansof a state equation, whereby the state vector x is composed from one ormore state variables. The state vector x(t) develops over time, wherebythe temporal development is generally described by means of a system ofdifferential equations. By means of appropriate transformation, thedifferential equations can be transferred to the general form of thestate equation x=f(x(t),u(t)), whereby x is the temporal derivative,u(t) the input vector of a system, which in the case of a controlledsystem, amongst other things, is very time-dependent, and f is generallya vector value function. These types of state variables also describethe state or the states of a system model, e.g. of the system modelconsisting of the RTP system and the object (semiconductor wafer,substrate). Furthermore, systems or system models are characterized byparameters whereby the system parameters generally do not develop overtime or no explicit temporal dependency can be given for the systemparameters. However, the parameters determine the transfer behavior ofthe system or of the system model, i.e. the relationship between inputand output values. Parameters are e.g. emissivity, transmissivity andreflectivity of the semiconductor wafer in the system model RTP systemsemiconductor wafer, whereas e.g. the wafer and radiation sourcetemperature (lamp temperature) are state variables.

The state of the system consisting of the object and the rapid heatingunit, and of the object is described as presented above, in general bymeans of a state vector which contains the state variable.

The process for determining a state variable from a model of an RTPsystem by means of at least one measurement signal measured on the RTPsystem—the measurement value—, which has a dependency upon the statevariable to be determined, comprises, in accordance with the invention,a measurement value forecast by means of the model—the predicted value—,whereby the measurement value and the forecast value respectivelycomprise components of a constant and a changeable or alternatingportion, and whereby respectively at least the changeable portion isdetermined separately by a filter, so as to form a first differencebetween the changeable portion of the measurement value and thechangeable portion of the measurement value forecast by the model, aparameter adaptation of at least one model parameter by recirculatingthe first difference into the model with the aim of adapting the modelbehavior to variable system parameters, formation of a second differencefrom the measurement value and the forecast value or from themeasurement value adjusted by the changeable portion and the adjusted orcorrected forecast value, state correction of a state of the modelsystem by recirculating the second difference into the model with theaim of bringing the state of the model system into correspondence withthat of the real system, and measuring at least one state variable onthe model.

Preferably, the state variable represents the temperature of thesemiconductor wafer or another value from which the temperature of thesemiconductor wafer can be clearly deduced.

The particular benefit of the above process in accordance with theinvention is that only one sensor e.g. a pyrometer, is required forrecording a measurement value, so as then to determine the state of thesystem consisting of the object (semiconductor wafer) and the rapidheating unit in such a way that e.g. the state of the object with regardto its temperature and/or any optical properties can be determined,which are a priori unknown system parameters, such as e.g., emissivity,transmissivity and/or reflectivity. Expressed in another way, theparticular benefit of the process in accordance with the invention isthat only one sensor e.g. a pyrometer, is required to record ameasurement value, in order to determine a priori unknown systemparameters such as emissivity, transmissivity and/or reflectivity of thesemiconductor wafer, whereby the system model is brought, by means ofparameter adaptation, to correspond as well as possible to thecontrolled path (the real system), and to make possible the statecorrection with which the states of observer and controlled path arebrought to correspond to one another. By means of the model adjustmentof the optical properties, the states of the system model and of thecontrolled path even remain consistent when the optical properties ofthe semiconductor wafer change (one talks of variable system parameterssuch as e.g. the reflectivity, transmissivity and emissivity of thesemiconductor wafer, because these parameters are temperature dependentand so implicitly time dependent with the time dependent temperature ofthe semiconductor wafer), by means of which the temperature derived froma state variable also lies close to the real temperature in thecontrolled path. A determination of the lamp or radiation sourceintensity by means of an additional detector, as described for examplein the previously specified DE-A-198 52 320, can then be dispensed with,and so the processes in accordance with the invention offer considerablesimplification with regard to accuracy of measurement and of technicalmeasuring complexity, and a considerable improvement to robustness,reliability and drift stability. Moreover, this invention allows almostinterference free determination of temperature, even with a high systemdynamic, i.e. with e.g. high heating and/or cooling rates of the wafer,and in particular with low wafer temperatures, and this is apre-requisite for reliable regulation of the rapid heating unit and soof the temperature of the semiconductor wafer, because any frequencycomponents (Fourier components) which result from the system dynamic,are also included in the forecast values of the model of the process inaccordance with the invention. This means that, even with a strongsystem dynamic, the forecast values and measurement values remainconsistent, and consequently the additional frequency portions caused bythe system dynamic must not be interpreted as interference. By means ofthis, these components can be separated from the actual modulationfrequency of the radiation sources, such as e.g. the lamps, by means ofwhich the susceptibility to interference and the efficiency of the rapidheating unit is considerably improved, in particular with high heatingrates. Heating rates of up to 500° C. can now be used in the laboratoryand partially in the domain of mass production in chip manufacture. Theprocess in accordance with the invention therefore preferably makes useof a pyrometer (or radiation detector) for the measurement of the waferradiation, because information such as e.g. the radiation sourceintensity (e.g. of the lamp radiation) is provided by the model. Sothat, however, e.g. the radiation source intensity can be taken from themodel with sufficient accuracy, a sufficiently accurate modeling of theheat emitters is required. If it is not possible to provide sufficientlyaccurate modeling of the heat emitters, the radiation source intensitycan be determined e.g. by means of an additional radiation detector,e.g. by means of a pyrometer which determines the radiation sourceintensity directly with sufficient accuracy, e.g. by means of the use ofappropriate aperture means, as they are described e.g. in patentapplication DE 19852321 tracing back to the applicant. The radiationsource intensity can, however, also e.g. be established by means of ameasurement of a value related to the intensity of the radiation source,whereby the radiation source intensity can then be produced by means ofsuitable conversion data. Instead of the conversion data, the radiationsource intensity can also be obtained with the help of an observer or ofan adaptive observer which comprises a radiation source model. Here, thevalue measured serves as a state correction of the radiation sourcestate and/or as parameter adaptation of parameters of the radiationsource model. FIG. 8 schematically shows the relationship between aninput value u(t) and a measured value y(t) for determining the radiationsource intensity. An input signal u(t) is given on a controller 200which controls the radiation sources 220 e.g. lamps corresponding to theinput signal. Between the controller and the radiation sources islocated a driver 210 which provides the corresponding input value u(t)for the corresponding power for operating the radiation sources. Theradiation sources, e.g. halogen lamps, then radiate the intensity I_(BB)in broadband, whereby a part of the radiation reaches the wafer 230. Thewafer is heated by this and then, by means of the wafer pyrometer, e.g.a narrow band signal 1 _(NB) is established which serves to establishthe wafer temperature. If the radiation source intensity is notdetermined by means of a sufficiently accurate modeling of the heatemitters with the exclusive use of the input signal u(t), as mentionedabove, additional measured values y(t) such as e.g. lamp voltage Vand/or lamp current I and/or lamp radiation intensity (broadband 1 _(BB)and/or narrowband 1 _(NB)) can serve to determine the radiation sourceintensity, whereby, as mentioned, these measured values y(t) can also beused to adjust a radiation source model from which the radiation sourceintensity is then obtained.

With the process for determining a state variable, the recirculation ofthe first difference preferably takes place using a first valuationfunction and a first control algorithm and/or the recirculation of thesecond difference using a second valuation function and a second controlalgorithm. The valuation functions here reproduce a gauge for thecorrespondence of the measured and forecast signal. The controlalgorithm then determines how the respective difference effects themodel, taking into account the valuation function, i.e. how the statesand/or parameters of the model are changed so as to reach the statecorrection and/or parameter adaptation so that the forecast value andmeasured value correspond to one another as closely as possible. Inorder to be able to compensate low frequency deviations moreeffectively, it is often beneficial to also use integrators in therecirculation branches as well as proportional corrections by means ofrecirculation matrices. The determination of a difference and therecirculation of the same into the system model for state correction orfor parameter adaptation is generally also called the determination of acontrol value within this application, with which the model states ormodel parameters can be influenced. In this connection therefore, theterm control value is extended in comparison to the term “control value”ordinarily used in control technology which means a system output valuecontrolled by means of a controller.

In another preferred embodiment of the process for determining a statevariable from a model of an RTP system by means of at least onemeasurement signal measured on the RTP system, the RTP system is a rapidheating unit with which an object, preferably a semiconductor wafer, isheated with radiation sources (heat emitters such as e.g. halogenlamps), and/or the model comprises at least one object heated in the RTPsystem, for example at least one semiconductor wafer, and forms a systemmodel. This type of RTP system is generally called a “cold wall reactor”because the heating of the wafer (object) takes please substantially bymeans of radiation energy from the heat emitters, and the wall of theRTP system is cold in the sense that the temperature of the wall issubstantially lower than the temperature of the wafer.

In general, however, the RTP system can also be a hot wall reactorwhereby the wall of the RTP system or the process chamber, in which theobject (e.g. the wafer) to be processed, is located, is generally at ahigher temperature than the object to be heated.

Preferably, the RTP system comprises different heat emitters which arerespectively actuated by means of an actuation value, whereby the heatemitters (or in general, the radiation sources) are preferably actuatedto modulate the radiated radiation intensity by means of the actuationvalue with different modulation parameters in order to clearly adaptseveral model parameters of the system model, such as for example thetransmissivity or reflectivity of a wafer. Because preferably, thesystem model, by means of the model parameters, takes into account theoptical properties of the wafer, whereby the optical properties of thewafer in the system model are then adjusted to the real opticalproperties of the wafer in the rapid heating unit. The heat emitters canbe combined into groups here, whereby the respective groups are thenactuated respectively with an actuation value.

The modulation of the radiation sources (e.g. heat emitters) can also beachieved or demonstrated by means of a continuous, not necessarilyperiodic stimulus, e.g. these generated stimuli can be caused by pseudorandom sequences (random stimuli) or colored noise, whereby thesesequences or the noise can be fed specifically to the set value of theheat emitters (or in general, to the radiation source or the radiationsources). The non-periodic stimuli can, however, also occur due toparasitic stimuli occurring in the system (therefore e.g. caused byinterference) which effect the set value of the heat emitters.Reasonable parameter adaptation is also possible by means of thisinvention in these cases.

In accordance with a particularly preferred embodiment of the invention,the measurement value comprises at least one heat radiation coming fromthe semiconductor wafer which is collected by a radiation detector,preferably a pyrometer. However, the heat radiation can also beestablished in other ways such as e.g. by means of a thermal element adefined distance away from the wafer and which measures a change intemperature caused by the heat radiation e.g. of a blackened surface. Apyrometer makes possible accurate determination of the radiationintensity and works contact free. The radiation signal collected here bythe pyrometer comprises at least one portion of the heat radiation ofthe wafer emitted from a measurement area on the semiconductor andradiation from the radiation sources reflected on the wafer andradiation transmitted independently of the wafer material and the wafertemperature through the wafer. Preferably, the radiation of theradiation sources has a modulation which allows a difference from thedirect heat radiation of the wafer. With this, it is possible toidentify the radiation reflected on the wafer and/or the radiationtransmitted through the wafer by means of modulation parameters of theradiation source modulation, as described in greater detail e.g. inpatents U.S. Pat. No. 6,191,392 and U.S. Pat. No. 6,369,363 tracing backto the applicant, whereby in this process, as already mentioned, atechnical measurement recording of the radiation source intensity can bedispensed with. When using modulated radiation sources (heat emitters),the measurement value comprises a changeable portion substantiallydependent upon the optical properties of the wafer, which is produced bythe modulation of the radiation sources, with which an adjustment of theoptical properties (preferably emissivity and/or transmissivity and/orreflectivity) can then be made using an algorithm which adjusts thechangeable portion in the measurement value recorded and in themeasurement value forecast by the system model by means of adaptation ofthe optical properties of the wafer (object) in the system model.

Alternatively or in addition to the above embodiment, the measurementvalue comprises radiation coming from an item e.g. contact free, bymeans of a pyrometer and/or the measurement value records thetemperature or a measurement value relating to the temperature of theitem by means of direct contact e.g. by means of a thermal element.Here, the item relates to the object, the semiconductor wafer, in such away that a temperature change of the object (semiconductor wafer) bringsabout the temperature change or a change to the measurement value of theitem in such a way, that e.g. by means of a model and/or a function fromthe knowledge of the state (e.g. temperature or of a measurement valuerelating to the temperature or of the measurement value) of the item,the temperature and/or the state of the object (wafer) can be concluded.The item can be e.g. a second wafer or a “cover plate”, whereby this isfixed over and/or below the actual wafer, a small distance away from thewafer, as illustrated in U.S. Pat. No. 6,051,512 or in U.S. Pat. No.6,310,328 tracing back to the applicant. Moreover, the item can be e.g.an area of the process chamber, a surface located near to a side of theobject or wafer which reflects at least part of the wafer radiation, anarea of a quartz disc (e.g. which is part of a quartz process chamber)which is positioned close to the object, or an object additionallyintroduced into the process chamber which reacts sensitively to anytemperature changes and/or to the temperature of the wafer (object) withregard to its measurement value. Preferably, in this embodiment as well,the RTP system comprises at least one heating device which is modulatedwith regard to the heat energy it gives out, and whereby the measurementvalue on an object is established which, due to its thermal properties(such as e.g. thermal mass) and/or its thermal coupling onto themodulated heating device (e.g. radiation source) only unsubstantiallyfollows, with regard to its temperature, the modulation of the heatingdevice, i.e. e.g. that a relative parameter (such as e.g. a modulationamplitude divided by the amplitude of the whole signal) for thetemperature modulation on the object is less than approximately 25%,preferably less than 10% or even less than 1% of the same relativeparameter for the modulation of the heating device. Preferably, theobject comprises or is a semiconductor wafer, a cladding (e.g. agraphite box, as made known in U.S. Pat. No. 5,837,555, U.S. Pat. No.5,872,889 tracing back to the applicant, and patent application DE 10156441 or a box as described in PCT/IB99/01946) which at least partiallysurrounds at least one semiconductor wafer), a chamber wall (or part ofa chamber wall) of a process chamber of the RTP system, or generally anitem close to the semiconductor wafer. Preferably, the measurement valueis recorded by means of a pyrometer and/or thermal element, and thestate variable established for the state is the temperature of theobject and/or the temperature of the semiconductor wafer, wherebypreferably, the measurement value is established on the semiconductorwafer and/or on an item near to the semiconductor wafer. Preferably alsoare the optical properties of the object such as e.g. the reflectivity,the transmissivity and/or the emissivity in the model are considered asmodel parameters.

With a preferred embodiment of the invention given as an example, thedetermination of the forecast value of the measurement value comprisesthe determination of a forecast value of the wafer radiation whichforecasts a portion caused by the wafer radiation on the pyrometersignal, i.e. the portion of the wafer radiation in the area of themeasurement point on the wafer which contributes to the measurementsignal of the radiation measuring unit. Because the signal recordedcomprises a radiation portion from the wafer as well as radiationportions from the radiation sources, i.e. the heat emitters, it isbeneficial for a clear state correction to separate the wafer and heatemitter portion. The state reconstruction or, in other words, thecorrect interpretation, is based here upon model forecasts from bothradiation portions. Here, the forecast of the signal portion of thewafer preferably comprises the determination of an intensity value ofthe heat radiation from the wafer in the area of a measurement wavelength of the pyrometer using the established state variables and anestablished emissivity of the wafer. Preferably, the forecast value ofthe wafer radiation is then determined using a model, taking intoconsideration the previously established intensity value of the waferradiation in the area of the measurement wave length of the pyrometerand of an established emissivity of the wafer. In this way, the portionon the pyrometer signal caused by the wafer is more beneficiallyforecast. Here, the model takes into consideration an influence of thechamber upon the effective emissivity of the wafer, because the chambergeometry and the reflectivity of the chamber walls can apparently havean effect which increases emissivity.

With a preferred embodiment of the invention given as an example, thedetermination of the forecast value of the measurement value furthercomprises, as well as determination of the wafer forecast value, thedetermination of a lamp forecast value (radiation source forecast value)and in general of a forecast value of the radiation from the radiationsources collected on the radiation measurement unit, which preferablyare lamps, e.g. halogen lamps of any form, flash lamps and/or arc lampsof any form or laser light sources. In general, radiation sources canalso be hot surfaces such as e.g. heated plates. The lamp forecast valueand radiation source forecast value forecasts a portion caused by theradiation sources on the pyrometer signal or detector signal. In thisway, a portion of the radiation coming from the radiation sources on thepyrometer signal, caused in particular by reflection and/or transmissionon the wafer, can be forecast, whereby parameters of thereflectivity/transmissivity of the wafer adapted to this are used. Here,the determination of the lamp (radiation source) forecast value arisingfrom the interaction between the wafer and the radiation sources (lamps)preferably comprises the determination of a broadband intensity value ofthe heat radiation of the wafer using the established state variable(e.g. the wafer temperature), taking into account an emissivity of thewafer. In order to improve the accuracy of the model forecast, theradiation interactions or other heat coupling mechanisms, such as e.g.heat convection and/or heat conduction between different objects (e.g.lamps, wafer, quartz elements within the process chamber or the processchamber or parts thereof) can generally be taken into consideration.Preferably the determination of the lamp forecast value furthercomprises the determination of an intensity value for the radiationsources using a lamp model or a radiation source model and the actuationvalue of the radiation sources. Because the states of the heat emittersdo not depend solely upon the set value of the same, but also aregenerally coupled together by means of broadband radiation interactions,it is beneficial also to take into account interactions of differentheat emitters so as to improve the accuracy of the forecast of thestates of the heat emitters. Here, the lamp and the radiation sourcemodel preferably takes into account interactions between the individualradiation sources themselves and/or with the wafer, whereby thebroadband intensity value of the heat radiation of the wafer is inputinto the input value of the lamp radiation source model. Furthermore,the lamp model preferably takes into account interactions between theindividual radiation sources such as e.g. between the lamps of a bank oflamps consisting of several lamps. The semiconductor wafer, as well asthe different radiation sources among themselves, interact with therespective intensity value of a radiation source. Here, the interactionsact, always temporally delayed, upon the intensity value of a radiationsource. As well as the power figure defined by the set value, theradiation interactions also cause an additional power figure which, likethe set value, determines the development over time of the emitterstate. By taking into account these interactions e.g. in the lamp orradiation source model, particularly accurate intensity values can beforecast for the individual radiation sources.

Because with this process, specific temperature values of thesemiconductor wafer should be used for controlling the temperature, allcalculations should be made in real time, preferably with fixedintervals of time. In order to fulfill the real time requirements, it istherefore advantageous to minimize the required computing power. Inorder to simplify the model for the lamps and radiation sources, and toreduce the required computing power, the radiation sources are thereforepreferably combined as groups, and the determination of the intensityvalue takes place for the respective groups. Here, the intensity valueis determined for the respective groups using at least one, preferablyhowever at least two representatives of the group in order to achieve ahigher level of accuracy. Here, the radiation sources are preferablyactuated at least within one group with the same actuation value.

When determining the lamp (heat emitter) forecast value, preferably amodel is used which forecasts the portion of the lamp radiation which isreflected on the wafer and if required is transmitted through the wafer,which falls in the visual field of the pyrometer, and this is using thedetermined intensity value of the radiation sources and an establishedemissivity of the wafer. Here, the model preferably establishes thereflectivity, and if required, the transmissivity of the wafer using theestablished emissivity in order to determine the reflected andtransmitted portion of the lamp radiation. Furthermore, the modelpreferably takes into account the chamber geometry in order also to takeinto account multiple reflections.

Preferably, the forecast value of the measurement value is formed byadding the wafer forecast value and the lamp (radiation source) forecastvalue, which should together forecast the measurement signal of thepyrometer. Here, the forecast value of the wafer radiation substantiallycontains a constant portion of the forecast value of the measurementvalue and the lamp forecast value substantially contains a constantportion and a changeable portion of the forecast value of themeasurement value. The changeable portion of the forecast value of themeasurement value substantially results from the modulation of theradiation of the radiation sources and the portion of the radiationreflected on the wafer and originating from the radiation sources, whichshould make it possible to distinguish between the two signals.

Preferably, for establishing the emissivity of the wafer, the forecastvalue of the measurement value is at least partially used. Here, theforecast value of the measurement value is preferably filtered so as toestablish the changeable portion of the same which substantiallycorresponds to the modeled portion of the radiation originating from theradiation sources and reflected on the wafer. In order to establish theemissivity of the wafer, an adaptive algorithm is preferably used whichadjusts the changeable portion (e.g. >1 Hz) of the forecast value of themeasurement value and adjusts a changeable portion of the radiationcoming from the semiconductor (which derives from at least onemeasurement point on the semiconductor wafer) recorded by the pyrometer.Because this adaptation algorithm only compares the changeable portions,the adaptation succeeds independently of the state of the real systemand the system model. The adaptation algorithm and the state correctiondo not therefore effect one another.

For a homogenization of the wafer temperature in the rapid heating unit,this is preferably set in rotation relative to the lamps and radiationsources, whereby the rotation (turning) can produce a changeable portionof the radiation coming from the semiconductor wafer, for example bymeans of inhomogeneities on the wafer (object or substrate) surface, orinhomogeneities (optical fluctuations i.e. inhomogeneities with regardto transmission and/or reflection) on a co-rotating wafer support device(wafer carrier which holds the wafer and, if required, sets it inrotation. This changeable portion is taken into account for establishinga good emissivity value, i.e. for adapting the parameters of the modeland/or in the model for establishing a state variable of the waferand/or of the rapid heating unit (e.g. when determining state variablessuch as e.g. the rotation speed and/or the rotation phase). Preferably,as described above, the emissivity established is then scaled before itis introduced to other processes in order to provide compatibility withregard to the values used.

With a preferred embodiment of the invention, the semiconductor wafer inthe model for establishing the state variable is seen as a so-calledblack body so that it is not necessary to establish emissivity forestablishing the state variable, and the model only requires theactuation value of the radiation sources and the determined statecorrection in order to establish the state variable.

The models used with this invention can be based upon physical models,i.e. the models describe the actual fundamental physical effects asaccurately as possible, or they can be empirical, i.e. e.g. described bymeans of a system transfer function. A description of the models bymeans of neural networks can also be beneficial. Moreover, several partmodels are preferably used which only in their entirety and by means oftheir reciprocal interaction form a total model of the object(substrate) of the system and rapid heating unit.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described in greater detail in the following using apreferred embodiment, given as an example, and with reference to thedrawings:

In the drawings:

FIG. 1 shows a schematic representation of a rapid heating unit withwhich the process in accordance with the invention can be used;

FIG. 2 shows a schematic representation of a part of the rapid heatingunit in accordance with FIG. 1 in which the angle of incidence oropening angle of a radiation sensor and the influence of differentelements in the rapid heating unit upon the signal measured from theradiation sensor are shown;

FIG. 3 shows a schematic representation of a temperature control in anRTP unit;

FIG. 4 shows a block diagram which shows a sequence of operation diagramfor determining a wafer temperature in a rapid heating unit;

FIG. 5 shows a schematic representation of one aspect of establishingthe wafer temperature in a rapid heating unit;

FIG. 6 shows a schematic representation of another aspect ofestablishing the wafer temperature in a rapid heating unit;

FIG. 7 shows a schematic representation of function blocks of a lampmodel which is used for establishing the wafer temperature in a rapidheating unit and

FIG. 8 shows a schematic representation of the relationship between aninput value u(t) and a measurement value y(t).

DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 shows a schematic representation of a rapid heating unit 1 forthe thermal treatment of a semiconductor wafer 2.

The rapid heating unit 1 has a housing 4 which consists of an upper wall6, a lower wall 7 and a side wall 8 located between these. The walls 6,7 and 8 together form a chamber 10. The chamber is divided by two quartzplates 12 into an upper chamber section 14, a middle chamber section 15,and a lower chamber section 16. In the upper and lower chamber sections14, 16, a number of radiation sources 18 are respectively provided inthe form of halogen lamps. Alternatively, or in addition, otherradiation sources, such as for example arc lamps, flash lamps or laserscan be provided, whereby the radiation sources have a high dynamic so asto make it possible to heat the wafer 2 quickly. The quartz plates 12are substantially permeable for the radiation from the radiation sources18.

The middle chamber section 15 forms a process chamber 15 in which thewafer 2 is held by means of a suitable holding device, not shown indetail. The holding device can comprise a rotation device for rotatingthe wafer 2, and which is able to rotate the semiconductor wafer 2within the process chamber, i.e. rotate the wafer relative to theradiation sources. In the process chamber section, the side wall 8 hasan insertion/removal opening 20 for loading and unloading thesemiconductor wafer 2. The insertion/removal opening 20 can be closedusing a suitable mechanism, not shown in detail. Preferably, but notnecessarily, there is a gas inlet opening 22 in the side wall 8 oppositethe insertion/removal opening 20 for introducing a gas into the middlechamber section 15, i.e. the process chamber section.

Within the process chamber 15, a compensation ring 24 is preferably alsoprovided which is able to compensate any marginal effects with regard totemperature distribution over the wafer during the thermal treatment.

Preferably, an opening for introducing a radiation measurement device26, in particular a pyrometer, is provided in the lower housing wall 7.The pyrometer 26 has a visual field directed at the wafer 2, and this isrepresented by a broken line in FIG. 1. The visual field is arranged insuch a way and has an opening angle such that radiation originatingdirectly from the radiation sources does not fall in the visual field ofthe pyrometer 26, or radiation of this type is only recorded by thepyrometer to a very reduced extent. However, radiation from theradiation sources reflected on the wafer 2 can fall in the visual fieldof the pyrometer, as shown schematically in FIG. 2 by means of the beamC.

FIG. 2 schematically shows a part of the rapid heating unit 1, and inparticular different radiation components which fall in the visual field(alpha) of the pyrometer 26. First of all, heat radiation comingdirectly from the wafer 2 falls in the visual field of the pyrometer, inso far as it originates from a point in the direct visual field of thepyrometer 26, as shown by the arrow A in FIG. 2. Furthermore, heatradiation from the wafer 2 falls in the visual field of the pyrometer26, and this is reflected on the lower chamber wall 7 and on the wafer 2itself, as shown by the dashed arrow B.

Moreover, radiation originating from the radiation sources 18 also fallsin the visual field of the pyrometer, whereby it is reflected on thewafer 2, as shown by the arrow C. Of course, different reflectionpatterns to those shown are possible, so that different radiationportions, both from the wafer and also from the radiation sources, fallin the visual field of the pyrometer. With an illustration in FIG. 2, itis assumed that the wafer 2 for the radiation of the radiation sources18 is substantially non-transparent. If this is not the case, radiationoriginating from the upper radiation sources 18 can also fall throughthe wafer 2 into the visual field of the pyrometer.

In order to make it possible to distinguish between the heat radiationfrom the wafer 2 and the radiation from the radiation sources 18reflected on the wafer 2, the radiation from the radiation sources 18has a modulation. Here, the modulation is chosen in such a way that theheat radiation of the wafer 2 does not follow this modulation. In orderto distinguish between radiation reflected on the wafer and transmittedthrough the wafer, radiation sources located above and below the wafercan have different modulation types such as modulation frequency and/ormodulation phase.

FIG. 3 shows a schematic representation of a temperature control of arapid heating unit which uses temperature determination in accordancewith this invention.

In FIG. 3, the rapid heating unit, which is also called an RTP unit(Rapid Thermal Processing unit), is shown by the block 30. A sensorsignal goes from the block 30 to a block 32 in which a temperaturedetermination takes place in accordance with this invention. The sensorsignal is preferably the signal from the pyrometer 26 which contains achangeable portion as well as a constant portion. With an opaque wafer,the changeable portion substantially originates exclusively from thelamp radiation reflected on the wafer, whereas the constant portionoriginates from the heat radiation from the wafer as well as from thelamp radiation reflected on the wafer. With silicon wafers, an opaquewafer is at temperatures of approximately over 600° C. so that anyradiation transmitted through the wafer, e.g. from a radiation sourceabove the wafer, is no longer relevant.

In block 32 the temperature of the wafer is determined by means of theprocess described in greater detail in the following. The establishedtemperature, which should represent the actual temperature of the wafer(T_(actual)) as well as possible, is forwarded to a control unit inblock 34. The control unit in the block 34 compares the actualtemperature (T_(actual)) with an incoming desired temperature value(T_(desired)) and, using the comparison, controls the actuation power ofthe lamps in the rapid heating unit 30. For this, e.g. an effectivevoltage (U_(eff)) is applied to the individual lamps. The control unitin the block 34 can have any controller, such as for example a PIDcontroller or a model-based controller which contains a forward control.In any case, the value of the actuation signal U_(eff) of the controlunit in block 34 is also forwarded to block 32 so as to be used for thetemperature determination. The temperature determination in block 32 isdescribed in greater detail below, with reference to FIGS. 4 to 7.

FIG. 4 shows, in block diagram form, the currently preferred embodimentof a process for establishing temperature.

The temperature is actually established in block 40. In block 40, thewafer temperature is established using a static chamber model whichincludes a model of the chamber, which includes at least a model of thechamber properties, preferably a model of the objects located in thechamber, preferably e.g. a wafer model, and optionally a lamp andradiation source model. In order to simplify the respective models,idealized parameters for the individual model are preferably used, atleast in part. The wafer in the wafer model is thus seen, for example,as a black emitter or a so-called black body with an emissivity of one.The effective voltage (U_(eff) lamps complete) which is applied to allof the lamps serves as an input value for establishing the wafertemperature, and this is for example fed from the control unit 34 inaccordance with FIG. 3 in block 40. The established wafer temperature isalso adapted using a state correction (control value) Z. This statecorrection can be understood to be a type of control circuit becausefrom measured values, and from those forecast by the model (theobserver), analogous to a desired/actual value comparison, a differenceor a correction value is established, whereby the set value of acontroller corresponds to the state correction. Alternatively or inaddition to the effective voltage applied to the lamps and radiationsources, any radiation source parameter can be used which is suitablefor making predictions about the energy radiated from the radiationsource. In this way e.g. the current or directly measured radiationvalues by means of which the radiation of the radiation sources can beestablished, can also be chosen.

The state correction (control value) Z is once again determined in block42, and it is proportional to a difference between a measured waferpyrometer signal (DC+AC)_(compl. measured) and a forecast waferpyrometer signal (DC+AC)_(compl. forecast). Block 42 can be in the formof a so-called P controller, whereby the correction would then beproportional to the error. In order to compensate low-frequency residualerrors, at least one I-controller is, however, generally added. Ofcourse, the controller can also be in the form of a PID controller. Themeasured wafer pyrometer signal corresponds to the sensor signalsupplied from block 30 to block 32 in accordance with FIG. 3. This waferpyrometer signal includes a constant portion and a changeable portion.The constant portion is substantially formed by radiation reflected onthe wafer, as shown by the arrow C in FIG. 2. In addition, the constantportion includes wafer radiation, i.e. heat radiation from the wafer anda constant portion of the lamp radiation reflected on the wafer and/oron the chamber walls of the process chamber and/or of the housing.

The forecast wafer pyrometer signal is a signal which is formed from aforecast value of the wafer radiation DC_(wafer forecast) and a lampforecast value (AC+DC)_(lamp refl. forecast). Here, the forecast valueof the wafer radiation substantially only includes a constant portion,whereas the lamp forecast value includes a constant and changeableportion.

The forecast value of the wafer radiation is determined from the wafertemperature T_(wafer) established in block 40. The established wafertemperature is first of all forwarded to a block 44. In block 44, aforecast intensity of the wafer radiation in the pyrometer measurementarea is determined, for example at 2.3 μm. The determination takes placeusing the wafer temperature T_(wafer) and an established emissivityE_(wafer scaled) of the wafer. Establishing emissivity is described ingreater detail below.

The forecast intensity of the wafer radiation I_(wafer 2.3) is thenforwarded to block 46. In block 46, the portion of the wafer radiationin the pyrometer signal is forecast, whereby the portion issubstantially a constant portion, but can also include a changeableportion if required. The forecast is made using a model into which theintensity of the wafer radiation in the pyrometer measurement area(I_(wafer 2.3)) and the established emissivity E_(wafer scaled) areentered as variable values. Here, the model also includes a model whichtakes into account the influence of the chamber upon the apparentemissivity of the wafer, i.e. an apparent increase in emissivity bymeans of the reflection properties of the process chamber and thechamber walls. The forecast portion of the wafer radiation in thepyrometer signal DC_(wafer forecast) represents the forecast value ofthe wafer radiation and is forwarded to an adding device in block 48where it is added to the lamp forecast value so as to obtain theforecast wafer pyrometer signal (DC+AC)_(complete forecast).

The lamp forecast value is established separately from the forecastvalue of the wafer radiation. Here, the intensity of the lamp radiationis first of all established using the effective voltage applied to thelamps or another suitable radiation source parameter with a lamp(radiation source) model, and this happens in block 50. The effectivevoltage applied to the lamps is supplied, for example, from the controlunit in block 34 in accordance with FIG. 3 to block 50. In order tosimplify the lamp model, the intensity is not determined for everyindividual lamp, of which, for example, over fifty can be provided inthe fast heating unit. Rather, the lamps are preferably divided intodifferent groups, for example four groups, whereby the lamps of eachgroup are substantially actuated respectively with the same lampvoltage. With the preferred embodiment given as an example, theintensity value is determined for the respective groups using at leasttwo representatives from the group.

The lamp model is built in such a way that it takes into accountinteractions between the respective lamp filaments. Furthermore, thelamp model takes into account interactions between the respective lampsand the wafer radiation. For this reason, when determining the intensityof the lamp radiation a forecast broadband intensity I_(wafer forecast)of the wafer radiation is entered into the lamp model as well as theeffective voltage applied to the lamps. The forecast broadband intensityof the wafer radiation is determined in block 52 using the wafertemperature T_(wafer) established in block 40 and, if so required, theestablished emissivity.

The components which go into the lamp model are shown again, forclarification, in FIG. 7. Here, the circle 54 forms the actual lampmodel. The lamp radiation is derived from the lamp model, as shown bythe circle 56.

An idealized lamp model goes into the lamp model 54, and this models theintensity of the lamp radiation in an open, endless space. However, acorrection parameter is also entered into lamp model 54 from the block60, and this takes into account the interactions between the individuallamp filaments of the lamps, in particular between adjacent lamps. Theseinteractions are schematically shown in the diagram shown in the lowerright hand corner of FIG. 7.

A second correction parameter from the circle 62 is also entered intothe lamp model 54, and this takes into account interactions between thelamp filament and the wafer 2. These interactions are also shown in theschematic representation.

The respective interactions between the lamp filaments themselves andbetween the lamp filaments and the wafer are established in advanceusing a reference sensor, as shown by circle 64. Instead of ameasurement taken by means of a reference sensor, it is also possible,of course, to provide a corresponding mathematical model for therespective interactions.

Reference is now made to FIG. 4 again, and the determination of the lampforecast value is explained in further detail. The intensity of the lampradiation I_(lamps) determined in block 50 is now forwarded to block 66.In block 66 the forecast portion of the lamp radiation in the pyrometersignal is determined. It is determined by means of a model which usesthe intensity of the lamp radiation I_(lamps) and the emissivityE_(wafer scaled) determined for the wafer as input values. The modelcontains a weighting for the portion of the individual lamps because thedifferent lamps have a different influence upon the pyrometer signal.The model takes into account the portion of the lamp radiation in thepyrometer measurement area reflected on the wafer which falls in thevisual field of the pyrometer, whereby the model takes into account thereflectivity of the wafer and the chamber geometry. The reflectivity ofthe wafer is once again established from the emissivity E_(wafer scaled)determined. It is substantially applicable that the reflectivity of thewafer equals one minus the emissivity, in so far as the wafer isnon-transparent for the lamp radiation.

The forecast portion of the lamp radiation in the pyrometer signal(AC+DC)_(lamp reflection forecast) is supplied as a lamp forecast valueto the adding unit in block 48 and added here to the forecast value ofthe wafer radiation. The lamp forecast value includes a constant portionand a changeable portion, whereby the changeable portion originates froma modulation of the lamp intensity, e.g. by modulation of the effectivevoltage applied.

As already mentioned, in block 48 the forecast value of the waferradiation is added to the lamp forecast value so as to produce theforecast wafer pyrometer signal which is supplied to block 42. In block42, a difference between the actually measured wafer pyrometer signaland the forecast wafer pyrometer signal is established, and a statecorrection (control value) Z determined from this which, once again, hasan influence upon the established wafer temperature T_(wafer) in block40. Here, the system is designed in such a way that the differenceconverges towards zero with the continuous cycle of the upper loops. Assoon as the difference is at zero or within a pre-defined toleranceinterval, it can be assumed that the established wafer temperatureT_(wafer) corresponds to the actual wafer temperature.

In several of the aforementioned function blocks, an “establishedemissivity” was used as an input value. It is explained in greaterdetail below, with reference to FIG. 4, how the established emissivitycan be determined.

As described above, in block 48 in accordance with FIG. 4, a forecastvalue of the wafer radiation is added to a lamp forecast value so as toobtain a forecast wafer pyrometer signal (DC+AC)_(compl. forecast). Thisforecast wafer pyrometer signal, which has a changeable as well as aconstant portion, is conveyed to a filter in block 90 in which theconstant portion is filtered out. The signal output from block 90 thusonly includes a changeable portion which substantially only originatesfrom the modulation of the lamp radiation. This signal is callAC_(lamp forecast). This signal is forwarded as an input value intoblock 92. As an additional input value, a filtered portion of the waferpyrometer signal measured is conveyed into the block 92. For this, thewafer pyrometer signal (DC+AC)_(compl. measured) is conveyed through afilter in block 92 so as to filter out the constant portion. Theresulting signal corresponds to the measured changeable portion of thewafer pyrometer signal AC_(measured) which is also conveyed as an inputvalue into the block 92. An emissivity value for the wafer is determinedin block 92 from the measured changeable portion of the wafer pyrometersignal and the forecast changeable portion of the wafer pyrometersignal. For this, an adaptive algorithm first of all adapts the opticalproperties of the system model (including e.g. emissivity, reflectivityand transmissivity of the wafer) so that the changeable portions (>1 Hz)of the measured wafer pyrometer signal and of the forecast waferpyrometer signal are covered. Because this adaptation algorithm onlyuses and compares the changeable portions of the measured waferpyrometer signal and the forecast pyrometer signal, the adaptationsucceeds independently of the state of the real system and the systemmodel, in particular independently of the temperature of the wafer(object). After the adaptation, the optical properties and in particularthe emissivity can be taken and measured from the system model.

Provided that the wafer is turned, i.e. rotated during the thermaltreatment, the wafer rotation can produce a changeable portioncorresponding to the rotation speed which, once again, can be taken intoconsideration during the determination of the emissivity value in block92. The changeable portion corresponding to the rotation speed can, forexample, be filtered out.

The emissivity value E_(wafer) established in block 92 is now forwardedto block 94 in which it is scaled for the subsequent processes, and issupplied as E_(wafer scaled) to the subsequent determination processes.

With the above emissivity determination, substantially only theemissivity in the measurement area of the radiation detector used, suchas for example the wafer pyrometer 26, is established, and this istypically 2.3 μm. With this determination it is assumed that thechangeable portions of the radiation signals from the measurement andfrom the forecast, which primarily originate from the modulation of theradiation sources, are substantially produced by reflection on the waferand reflection on the chamber walls. For this reason, the reflectivityof the wafer is an important factor in the adaptation, described above,of the optical properties by means of the adaptation algorithm. Ofcourse, the transmissivity of the wafer can also assume an importantrole here provided that the wafer for the heat radiation is not opaque.

FIG. 5 shows a simplified representation of a system for determining thetemperature of a semiconductor wafer in a rapid heating unit or fordetermining a state or a state variable. In FIG. 5, the same referencenumbers are used as in the previous figures in so far as similar orequivalent elements are described.

FIG. 6 shows a simplified representation for determining the emissivityor for determining model parameters. As described in FIG. 4, with theprocesses in accordance with the invention, the determination of atleast one state variable (e.g. the wafer temperature) and thedetermination or adaptation of at least one model parameter (e.g.emissivity) run parallel, whereby the state is determined by means of anobserver which is represented in simplified form in FIG. 5 by functionblocks 76, 72, 82, 84 and 86. The adaptation of the model parameters isimplemented using an adaptive observer which is described schematicallyin FIG. 6 by means of function blocks 104, 102, 112, 110 and 108.

In order to illustrate the invention presented in FIG. 4 again, in thefollowing the state determination and the parameter adaptation by meansof the observers schematically represented in FIGS. 5 and 6, aredescribed separately from one another once again, whereby in the processin accordance with the invention shown in FIG. 4, as mentioned, thestate determination and parameter adaptation run in parallel. Asequential process of the state and parameter determination would alsobe possible if e.g. different successive measurement values and theforecast values of the same are established, i.e. e.g. so thatchangeable and constant portions of a measurement signal aresuccessively established, unlike in the embodiment in FIG. 4, and usedfor determining the state of parameter.

In FIG. 5, a rapid heating unit 1 with heating lamps 18 is schematicallyrepresented. A semiconductor wafer 2 is located in the rapid heatingunit 1 for the thermal treatment of the same. A pyrometer 26 is directedto one side of the wafer.

The heating lamps 18 are actuated by an actuation unit 70.

During the thermal treatment of the wafer 2, radiation coming from thewafer, which includes wafer radiation as well as radiation reflected onthe wafer, is measured in the pyrometer 26, and the measurement signalis forwarded to the block 72. The measurement signal is alsoschematically illustrated by 74.

As well as the actual rapid heating unit 1, in the box 76 defined by abroken line, a model of a rapid heating unit 1′ is shown. The featuresof the model rapid heating unit are respectively identified with anapostrophe ′. The model of the rapid heating unit 1′ includes e.g. amodel of the lamps 18′, a model of the wafer 2′, a model of the chamber4′ and a model of the pyrometer 26′. The actuation signal of the heatinglamps 18 is entered in the model of the fast heating unit 1, as shown bythe broken line 78. By means of the block 80, which is a part of thewhole model, a temperature T of the wafer 2′ is given in the model asunit 1′, and said temperature has an influence upon the states of thewafer model and the states of the other models and/which has the modelof the wafer 2′ and the other models. Using the actuation power and thepre-specified temperature T for the wafer 2′, the model of the rapidheating unit 1′ calculates a forecast pyrometer signal(DC+AC)_(comp. forecast) and transfers this to block 82. The measuredpyrometer signal from block 72 and the forecast pyrometer signal 82 areboth transferred in block 84, in which a difference between these twovalues is calculated. From the difference, a state correction (controlvalue) is then determined which is transferred into block 80 so as tochange the temperature value T determined there (which is in the form ofa state variable of a state of the model/s) of the wafer 2′ in themodel, taking into account the state correction. The temperature T isalso issued from the model to circle 86 and can be used, for example,for a temperature regulation or temperature control outside of themodel. The system shown in FIG. 5 continuously, or at pre-specifiedintervals of time, compares (e.g. by means of a key frequency) themeasured pyrometer signal and the pyrometer signal forecast from themodel, and tries to regulate the difference to zero by selectingappropriate states of the models. If the difference is zero or within atolerance range, the modeled wafer temperature T in the circle 86corresponds to the actual wafer temperature which can thus beestablished using a single wafer pyrometer 26.

The modeled radiation intensity 88 is located opposite the actualradiation intensity shown by 74, and in accordance with the model, theformer can be divided into wafer radiation and lamp radiation, becausethe respective contributions can be identified from the model forecasts.

FIG. 6 shows an alternative representation of a system for determiningthe emissivity in accordance with this invention, whereby the form ofthe representation is similar to that of FIG. 5. For this reason, thesame reference numbers are used in FIG. 6 as in FIG. 5 in so far as thesame or equivalent parts are being described. FIG. 6 once again shows aschematic representation of a rapid heating unit 1 with a housing 4, aswell as radiation sources 18 and a semiconductor wafer 2 held in thesame. Furthermore, a pyrometer 26 is shown once again. The heating lamps18 are once again actuated by means of an actuation unit 70.

100 represents the actually measured radiation intensity of thepyrometer 26, whereby in FIG. 6, only the changeable portion is shown.This changeable portion AC_(measured) is also forwarded from thepyrometer 26 to a block 102.

In a block 104, a model of the rapid heating unit is shown once again,whereby the model elements are shown with an apostrophe ′. The model ofthe rapid heating unit 1′ comprises a model of the wafer 2′, the chamber4′, the heating lamps 18′ and the pyrometer 26′.

The actuating power of the actuating unit 70 is fed into this model, asindicated by the broken line 78. In the box 104 there is also a block106 in which the emissivity of the wafer is determined at 2.3 μm, andthis is entered into the model of the wafer 2′ and issued to the oval(interface) 108. A changeable portion of the pyrometer signal is nowforecast AC_(forecast) within the model using the actuating powerapplied to the rapid heating unit 1. This signal is transferred to block110, and from there to block 112. The signal AC_(measured) from block102 is also transferred into block 112. In block 112, a differencebetween the actually measured changeable portion of the pyrometer signaland the forecast changeable portion of the pyrometer signal isdetermined, and from this difference a control parameter is establishedwhich is supplied to block 106. In block 106, and using the controlparameter, the emissivity is changed as a state variable of the wafer(or more accurately, as a parameter of the system model), and fed bothinto the model of the wafer 2′ and also issued to the oval (aninterface) 108. It should be noted that a change to emissivity of coursealso entails a change to other optical properties, such as thereflectivity and/or transmissivity in the model, although one will notgo into detail here.

The system is once again designed in such a way that it tries to reducethe difference AC to zero or to a value within a pre-defined toleranceinterval, so that the modeled emissivity corresponds with the actualemissivity of the wafer.

The various models used previously can be designed in different ways.With the lamp model, a calibration of the lamp model, and in particularthe effect of each individual lamp upon the model, and the weighting ofeach lamp with regard to the forecast pyrometer signal can be determinedusing a calibration process. With this type of calibration process,individual lamps can respectively be operated, and the lamp radiationemitted from these can be measured. This can take place with and withouta wafer in the rapid heating unit. With a wafer in the rapid heatingunit, the weighting factor is established for the forecast pyrometersignal of the lamps, whereas without a wafer, the pure radiationintensity of the lamp with a specific actuation power is established.

In summary, with regard to one aspect of the invention, it is possibleto develop a model which gives a good dynamic description of the processparameters in an RTP chamber. Here, a substantial uncertainty can beassociated with the model in the optical parameters of a wafer locatedin the chamber. By using changeable portions of the heat radiationproduced by module actuated heat emitters, the optical parameters of themodel can be adapted to those of the real system in the aforementionedmanner. Because this adaptation only takes into account the changeableportions of the radiation in the chamber, it is substantiallyindependent of the state (e.g. the temperature) of the wafer. Followingadaptation, the uncertainty of the model with regard to the opticalparameters of the wafer is eliminated, and the model and the real systemhave almost identical transfer behavior (actuation value of the heatemitters to the measured pyrometer signal and forecast pyrometersignal). The initial state of the real system, in particular the wafertemperature, does not necessarily correspond, however, to the initialstate of the system model. This difference is reflected in a differencebetween the measured pyrometer signal and the forecast pyrometer signal,and with the same signs and proportional for small differences. For thisreason, a state correction is made using this difference. In the endeffect, the model parameters are thus adjusted to the parameters of thereal system, and furthermore, the state of the model also follows thatof the real system within tight boundaries. For this reason, a statevariable, such as for example the wafer temperature, can be takendirectly from the model and measured here.

Moreover, in the previously described system, a process can beintegrated whereby irregularities on one side of the semiconductorwafer, such as for example points, to which the pyrometer is directed,are identified before loading the wafer into the rapid heating unit 1.This can be achieved by scanning said surface and mapping theirregularities. For example, the individual layers of a pile can beestablished by a multi-point measurement. These values are entered intothe temperature calculation model so that the irregularities areidentified and correspondingly compensated.

In this way, the emissivity of the wafer can be calculated at anyindividual temperature and is available for a corresponding controldevice or the model.

The measurement and mapping of the rear side can be carried out atambient temperature by means of a spectral ellipsometer in real time,while the wafer waits for its thermal treatment. Another possibilitywould be a surface reflection measurement and mapping of the upper sideor the surface, which can also be done at ambient temperature.

This process, which can supply information for the temperaturecalculation model, can alternatively also be used in a conventionalsystem for determining the temperature of a wafer.

Although the invention was previously described using a preferredembodiment given as an example, it should be noted that the invention isnot limited to the specifically shown embodiments, and in particular,also comprises embodiments which result from combining and/or changingfeatures of individual embodiments.

The specification incorporates by reference the disclosure of Germanpriority document 102 60 673.0 filed Dec. 23, 2002, DE 103 29 107.5filed Jun. 27, 2003, and PCT/EP2003/013387 filed Nov. 28, 2003.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. A method of determining at least one condition variable from a modelof an RTP system by means of at least one measurement signal, themeasurement value, detected at the RTP system and having dependency uponthe condition variable that is to be determined, and by means of ameasurement value, the predicted value, predicted by means of the model,wherein the measurement value and the predicted value each comprisecomponents of a constant portion and a changeable portion, the methodincluding the steps of separately establishing at least the changeableportion by a filter to form a first difference between the changeableportion of the measurement value and the changeable portion of themeasurement value predicted by the model; adapting at least one modelparameter by feeding the first difference back into the model with theaim of adapting the model behavior to variable system parameters;forming a second difference from the measurement value and the predictedvalue, or from the measurement value corrected by the changeable portionand the predicted value corrected by the changeable portion; correctinga condition of the model system by feeding the second difference backinto the model with the aim of bringing the condition of the modelsystem into correspondence with that of the real system; and detectingat least one condition variable from the model.
 2. A method according toclaim 1, wherein the feeding of the first difference back takes place bymeans of a first valuation function and a first control algorithm and/orthe feeding of the second difference back takes place by means of asecond valuation function and a second control algorithm.
 3. A methodaccording to claim 1, wherein the RTP system is a rapid heating unitwith which a semiconductor wafer, is heated with radiation sources,and/or the model includes at least one semiconductor wafer heated in theRTP system and forms a system model.
 4. A method according to claim 3,wherein in order to modulate radiation sources by means of an actuationvalue, different radiation sources are actuated with differentmodulation parameters to clearly adapt transmissivity and/orreflectivity parameters, of a semiconductor wafer.
 5. A method accordingto claim 4, wherein modulation is produced and represented by acontinuous, though not necessarily periodic, stimulus by means of pseudorandom sequences, colored noises, or by stimuli of a set value of theradiation sources caused parasitically in the system by interference. 6.A method according to claim 1, wherein the condition variable comprisesat least a temperature of a semiconductor wafer.
 7. A method accordingto claim 1, wherein the system model takes into account the opticalproperties of a wafer by means of model parameters, and wherein opticalproperties of the wafer in the system model are adjusted to the realoptical properties of the wafer in a rapid heating unit.
 8. A methodaccording to claim 5, wherein the measurement value has a changeableportion that depends substantially upon optical properties of a waferand is produced by a modulation of the radiation sources, and whereinadjustment of the optical properties takes place by means of analgorithm that adjusts the changeable portion in the detectedmeasurement value and that of the predicted measurement by adaptation ofoptical properties of the wafer in the system model.
 9. A methodaccording to claim 8, wherein the optical properties of the wafercomprise the emissivity and/or the reflectivity and/or thetransmissivity.
 10. A method according to claim 3, wherein themeasurement value comprises at least radiation that is coming from asemiconductor wafer and that is collected by a pyrometer.
 11. A methodaccording to claim 10, wherein the collected radiation comprises atleast heat radiation from the semiconductor wafer and radiation from theradiation sources reflected at the semiconductor wafer.
 12. A methodaccording to claim 1, wherein determination of the predicted value ofthe measurement value comprises determination of a predicted value of asemiconductor wafer radiation which predicts a portion of a pyrometersignal caused by the wafer.
 13. A method according to claim 12, whereinthe determination of the predicted value of the wafer radiationcomprises determination of an intensity value of a semiconductor waferradiation in the area of a measurement wavelength of the pyrometer usingthe established condition variable and an established emissivity of thesemiconductor wafer.
 14. A method according to claim 13, wherein thedetermination of the predicted value of the wafer radiation is effectedusing a model, taking into account the intensity value of the waferradiation in the area of the measurement wavelength of the pyrometer andan established emissivity of the semiconductor wafer.
 15. A methodaccording to claim 14, wherein the model takes into account an influenceof a rapid heating unit chamber upon the established emissivity of thesemiconductor wafer.
 16. A method according to claim 12, wherein thedetermination of the predicted value of the measurement value comprisesdetermination of a lamp predicted value which predicts a portion of apyrometer signal caused by radiation sources.
 17. A method according toclaim 16, wherein the determination of the lamp predicted valuecomprises the determination of a broadband intensity value of the heatradiation of the semiconductor wafer using the established conditionvariable and an established emissivity of a semiconductor wafer.
 18. Amethod according to claim 16, wherein the determination of the lamppredicted value comprises the determination of an intensity value of theradiation sources using a lamp model and the actuation value of theradiation sources.
 19. A method according to claim 18, wherein the lampmodel takes into account interactions between the semiconductor waferand the individual radiation sources.
 20. A method according to claim19, wherein the lamp model uses a predicted broadband intensity value ofthe heat radiation of the semiconductor wafer as an input value.
 21. Amethod according to claim 18, wherein the lamp model takes into accountinteractions between the individual radiation sources.
 22. A methodaccording to claim 18, wherein the radiation sources are combined asgroups and an intensity value for the radiation sources is determinedfor the respective groups.
 23. A method according to claim 22, whereinthe determination of the intensity value for the radiation sources forthe respective groups is effected using at least two representatives ofthe group.
 24. A method according to claim 22, wherein the radiationsources are actuated at least within one group with the same value. 25.A method according to claim 16, wherein when determining the lamppredicted value, a model is used that predicts the portion of the lampradiation that is reflected at the semiconductor wafer and that falls inthe visual field of the pyrometer, and wherein this is accomplishedusing a determined intensity value of the radiation sources and anestablished emissivity of the semiconductor wafer.
 26. A methodaccording to claim 25, wherein the model establishes the reflectivity ofthe semiconductor wafer.
 27. A method according to claim 26, wherein thereflectivity is established using the established emissivity.
 28. Amethod according to claim 25, wherein the model takes into account thechamber geometry of a rapid heating unit.
 29. A method according toclaim 16, wherein the predicted value of the measurement value is formedby adding the predicted value of the wafer radiation and the lamppredicted value.
 30. A method according to claim 29, wherein thepredicted value of the wafer radiation essentially includes a constantportion of the predicted value of the measurement value, and wherein thelamp predicted value essentially includes a constant portion and achangeable portion of the predicted value of the measurement value. 31.A method according to claim 12, wherein the emissivity of thesemiconductor wafer is established at least partially from the predictedvalue of the measurement value.
 32. A method according to claim 31,wherein the predicted value of the measurement value is filtered toestablish the changeable portion thereof that essentially corresponds tothe modulated portion of the radiation originating from radiationsources and reflected at the semiconductor wafer, which radiation fallsin the pyrometer from a measurement point on the semiconductor wafer.33. A method according to claim 32, wherein the emissivity of thesemiconductor wafer is established using an adaptive algorithm thatcompares the changeable portion of the predicted value of themeasurement value and a changeable portion recorded by the pyrometer andoriginating from the radiation of at least one measurement point on thesemiconductor wafer.
 34. A method according to claim 3, wherein asemiconductor wafer is rotated in the rapid heating unit, and a rotationspeed and/or a rotation phase in the model is taken into account forestablishing the emissivity and/or optical fluctuations of the waferand/or of a wafer carrier of the semiconductor wafer.
 35. A methodaccording to claim 34, wherein an established emissivity is scaledbefore it is taken on to other processes.
 36. A method according toclaim 3, wherein a semiconductor wafer in the model for establishing acondition variable is seen as a black body.
 37. A method according toclaim 1, wherein the RTP system comprises at least one heating devicethat is modulated with regard to the heat energy it gives out, andwherein the measurement value is established on an object that, due toits thermal properties and/or its thermal coupling to the modulatedheating device, only immaterially follows the modulation of the heatingdevice with regard to its temperature.
 38. A method according to claim37, wherein the object is a semiconductor wafer, a cladding that atleast partially surrounds at least one semiconductor wafer, a chamberwall of a process chamber of the RTP system, or a item in the vicinityof a semiconductor wafer.
 39. A method according to claim 1, wherein themeasurement value is established by means of a pyrometer and/or athermocouple element.
 40. A method according to claim 39, wherein thecondition variable is the temperature of the object.
 41. A methodaccording to claim 40, wherein the condition variable is the temperatureof a semiconductor wafer, and wherein the measurement value isestablished on the semiconductor wafer and/or on an item in the vicinityof the semiconductor wafer.
 42. A method according to claim 1, whereinthe model parameters comprise reflectivity, transmissivity and/oremissivity properties of the semiconductor wafer.